Magnetic tape systems commonly exhibit instantaneous speed variations (ISV) that are distributed in the frequency spectrum from low frequencies that are mostly excited mechanically to high frequency ISV events that are due to tape phenomena. Certain tape drives and associated tape transducers have a sensitivity to ISV that occur in the 7 KHz to 10 KHz range. For certain tape drive units and associated transducer circuitry operating on 1/4-inch wide tape running at about 34 Inches Per Second (IPS), such sensitivity to ISV is attributable, in part, to the coherent longitudinal wave which is generated in the tape that affects the relative position of a recorded signal, and that translates to a time-related and positionally-oriented error which, in turn, affects the accuracy with which the transducer circuitry can record and reproduce signals.
One mechanically resonant system that is responsible for ISV includes a length of tape under tension that passes from one tangent point on a tape reel to another tangent point on another tape reel, with the excitation force being created by the unwinding or peeling of the tape layers at a rate determined by the longitudinal velocity of the tape. Specifically, this excitation is attributable to an interaction of the magnetic coat and back coat of the tape, and to the friction interaction of those surfaces as the tape unwinds. One scheme to reduce this mode of ISV simply lengthens the tape path to reduce the characteristic frequency of the ISV events. However, because of packaging constraints, particularly in tape cartridges, the scheme of lengthening the tape path is not practical.
Another scheme to reduce this mode of ISV modifies the back coat or the magnetic coat of the tape in order to reduce the excitation forces due to friction. However, reducing the frictional interaction of the magnetic coat and back coat can have adverse effects on tape windability and the orderly packing of tape on a reel.